Search results for "fluid"
showing 10 items of 5513 documents
Superconductivity with broken time-reversal symmetry inside a superconducting s-wave state
2018
In general, magnetism and superconductivity are antagonistic to each other. However, there are several families of superconductors, in which superconductivity may coexist with magnetism, and only a few examples are known, when superconductivity itself induces spontaneous magnetism. The most known compounds are Sr$_2$RuO$_4$ and some noncentrosymmetric superconductors. Here, we report the finding of a narrow dome of a novel $s+is'$ superconducting (SC) phase with broken time-reversal symmetry (BTRS) inside the broad $s$-wave SC region of the centrosymmetric multiband superconductor Ba$_{\rm 1-x}$K$_{\rm x}$Fe$_2$As$_2$ ($0.7 \lesssim x \lesssim 0.85$). We observe spontaneous magnetic fields …
Dynamics of a Ferromagnetic Particle Levitated Over a Superconductor
2018
Under conditions where the angular momentum of a ferromagnetic particle is dominated by intrinsic spin, applied torque is predicted to cause gyroscopic precession of the particle. If the particle is sufficiently isolated from the environment, a measurement of spin precession can potentially yield sensitivity to torque beyond the standard quantum limit. Levitation of a micron-scale ferromagnetic particle above a superconductor is a possible method of near frictionless suspension enabling observation of ferromagnetic particle precession and ultrasensitive torque measurements. We experimentally investigate the dynamics of a micron-scale ferromagnetic particle levitated above a superconducting …
Interference of nonequilibrium quasiparticles in a superconductor
2003
Abstract We have observed an interference of nonequilibrium quasiparticles, injected from a copper electrode into an aluminium loop through a tunnel barrier. At temperatures below 1K the tunnel current at fixed voltage bias is periodically modulated by external magnetic field. The amplitude of the modulation reaches maximum at a bias slightly below the gap energy, and decreases with the further increase of the bias voltage. For a given voltage bias the amplitude of the current oscillations decreases with increase of the temperature and the loop circumference.
Force-free state in a superconducting single crystal and angle-dependent vortex helical instability
2017
Superconducting 2H-NbSe2 single crystals show intrinsic low pinning values. Therefore, they are ideal materials with which to explore fundamental properties of vortices. (V, I) characteristics are the experimental data we have used to investigate the dissipation mechanisms in a rectangular shape 2H-NbSe2 single crystal. Particularly, we have studied dissipation behavior with magnetic fields applied in the plane of the crystal and parallel to the injected currents, i.e. in the force-free state where the vortex helical instability governs the vortex dynamics. In this regime, the data follow the elliptic critical state model and the voltage dissipation shows an exponential dependence.Moreover,…
Light-induced superconductivity
2016
Intense light pulses irradiating a sample of K3C60 result in dramatic changes of its high-frequency (terahertz) conductivity. Could these be signatures of fleeting superconductivity at 100 K and beyond?
Energy dependence of the electron-boson coupling strength in the electron-doped cuprate superconductor Pr1.85Ce0.15CuO4−δ
2017
In the conventional theory of superconductivity the critical temperature Tc is determined by the electron-phonon coupling constant and the phonon cut-off frequency. The hallmark experiments of McMillan and Rowell demonstrated that bosons (phonons) responsible for pairing can be observed through the frequency dependence of the gap parameter. Determination of the electron-boson coupling strength in high-${T}_{c}$ cuprates is, however, not an easy task. One of the promising ways is to measure the energy relaxation rate of photoexcited carriers by using femtosecond real-time techniques. Here, considering the electron relaxation process within the conduction band, it is commonly assumed that the…
Robust semi-Dirac points and unconventional topological phase transitions in doped superconducting Sr2IrO4 tunnel coupled to t2g electron systems
2017
Semi-Dirac fermions are known to exist at the critical points of topological phase transitions requiring fine-tuning of the parameters. We show that robust semi-Dirac points can appear in a heterostructure consisting of superconducting Sr2IrO4 and a t2g electron system (t2g-ES) without fine-tuning. They are topologically stable in the presence of the symmetries of the model, metallic t2g-ES and a single active band in Sr2IrO4. If the t2g metal is coupled to two different layers of Sr2IrO4 (effectively a multiband superconductor) in a three-layer-structure the semi-Dirac points can split into two stable Dirac points with opposite chiralities. A similar transition can be achieved if the t2g-E…
Distinguishing Majorana Zero Modes from Impurity States through Time-Resolved Transport
2019
We study time-resolved charge transport in a superconducting nanowire using time-dependent Landauer-B{\"u}ttiker theory. We find that the steady-state Majorana zero-bias conductance peak emerges transiently accompanied by characteristic oscillations after a bias-voltage quench. These oscillations are absent for a trivial impurity state that otherwise shows a very similar steady-state signal as the Majorana zero mode. In addition, we find that Andreev bound states or quasi-Majorana states in the topologically trivial bulk phase can give rise to a zero-bias conductance peak, also retaining the transient properties of the Majorana zero mode. Our results imply that (1) time-resolved transport m…
Highly sensitive superconducting circuits at ∼700 kHz with tunable quality factors for image-current detection of single trapped antiprotons
2016
We developed highly-sensitive image-current detection systems based on superconducting toroidal coils and ultra-low noise amplifiers for non-destructive measurements of the axial frequencies (550$\sim$800$\,$kHz) of single antiprotons stored in a cryogenic multi-Penning-trap system. The unloaded superconducting tuned circuits show quality factors of up to 500$\,$000, which corresponds to a factor of 10 improvement compared to our previously used solenoidal designs. Connected to ultra-low noise amplifiers and the trap system, signal-to-noise-ratios of 30$\,$dB at quality factors of > 20$\,$000 are achieved. In addition, we have developed a superconducting switch which allows continuous tu…
Collective amplitude mode fluctuations in a flat band superconductor formed at a semimetal surface
2016
We study the fluctuations of the amplitude (i.e., the Higgs-Anderson) mode in a superconducting system of coupled Dirac particles proposed as a model for possible surface or interface superconductivity in rhombohedral graphite. This system also serves as a generic model of a topological semimetal with an interaction-driven transition on its surface. We show that the absence of Fermi energy and vanishing of the excitation gap of the collective amplitude mode in the model leads to a large fluctuation contribution to thermodynamic quantities, such as the heat capacity. As a consequence, the mean-field theory becomes inaccurate, indicating that the interactions lead to a strongly correlated sta…